The three-position actuator is intended for use with a movable control element, such as a valve having three control positions. An example of such use is in an automotive vehicle, where the valve may be in the heating-cooling system. The actuator is designed to operate from manifold vacuum, where pressure differentials between manifold vacuum and atmospheric pressure are used.
The first embodiment of the invention relates to a specific improvement in a flexible connector adapted to interconnect a movable spring seat and a plate connected to the central portion of a flexible diaphragm. The flexible connector is in the form of a thin plastic strap which conveniently may be polyethylene terephthalate available under the Dupont trademark MYLAR. The strap is substantially inextensible but is highly flexible so that it does not oppose approach between the plate and seat.
In order to protect the flexible plastic strap, rigid curved guide means are provided by the plate and seat engageable by portions adjacent the ends of the strap, so that as it is subjected to tension, end portions conform to curved guides, which prevent stress concentration.
Preferably the construction by which the ends of the straps are connected to the flat plate and seat members comprises a central opening in the associated member and a tab forming cut-out adjacent to but spaced laterally from the central opening. The cut-out is formed so that the tab, when bent into arcuate configurations toward the other member and toward the opening, forms a second opening in the member through which the end portion of the strap is extended. This end portion of the strap is provided with an opening and is brought into flat surface-to-surface contact with the surface of the member remote from the other member. The end portion of the strap is then firmly attached to the outer surface of the member by fastening means, such as a rivet which passes through the central opening in the member and in the end portion of the strap. The rivet connecting one end of the strap to the associated member serves to connect a member with an actuating rod, and in a preferred embodiment of the invention, the rivet is provided as an integral portion of the inner end of the rod.
As thus far described the spring seat may be mounted on a second diaphragm generally similar to the first diaphragm and movable in the chamber as a result of pressure differentials applied to opposite sides of the second diaphragm.
However, in a preferred embodiment of the invention only a single diaphragm is provided in the casing and divides the casing into two sealed pressure chambers, each of which is provided with a connection to an external pressure source, ordinarily a source of subatmospheric pressure or vacuum. In this embodiment of the invention an actuating rod extends into the casing and has its inner end connected to flat plate means which in turn is connected to the central portion of the diaphragm. A first compression spring is provided interposed between the end of the casing through which the actuating rod is movable and the plate. At the other side of the diaphragm there is provided a floating spring seat which is interconnected to the plate by a connector adapted to limit separation between the spring seat and plate but to provide no forces opposing approach between the seat and plate. The connector in this embodiment of the invention may be, and preferably is, the improved connector as previously described.
Prior U.S. Pat. No. 3,709,461 to Johnson, discloses a three position actuator using two diaphragms and essentially different means for limiting separation between the diaphragms, one of which serves as a spring seat.